The Colour Is Green

A top secret chemical called 12X, used for in rocket fuel, is being transported to a new international space base in Cornwall. A UFO evades interception and is tracked heading for the area. Destroying the escort, the Aliens hi-jack the tanker and take it to a disused chemical works. It seems a component of the 12X is a condensed green gas which is also what the Aliens use to breath on their journeys, and Straker must prevent them from obtaining it. Using a dummy alien spacesuit, Straker infiltrates the Alien operation and substitutes a green coloured liquid for the fuel. The Aliens depart but realise the deception and return, destroying the tanker before Sky 1 destroys it. The Aliens have been defeated but the space programme has also been put back...